170 FLIGHT International, 1 August 1963
FLEXIBLE WINGS
AT WORK
Largest Flex-Wing aircraft so far built, the Fleep
is a prototype of a manned transport for battlefield
use. Standing beside it during the handing-over
at the Ryan factory is Mr M. M. McDaniel, Flex
Wing programmes manager
IN 1961 the Ryan Aeronautical Co, of San Diego 12, Calif,
• started full-scale flight tests with the first Flex-Wing aircraft,
to demonstrate the feasibility of the idea. The idea was not
new, but Ryan was the first to put it into practice: to build an
aeroplane with a wing consisting of a delta-shaped flexible, plastics-
covered sheet attached to a rigid leading edge and centreline.
Under load the sheet billows out into port and starboard planes
each forming part of the surface of a cone. Such a wing has no
proper aerofoil section; in fact it is essentially two-dimensional.
But it is light and cheap, and for many specialist tasks appears
superior to a conventional "rigid" aerofoil. Aircraft control is
accomplished not by aerodynamic reaction on movable surfaces
but by displacing the suspended-body e.g. position relative to the
wing.
During the latter part of 1961 Ryan were content to carry on
proving the principle, which the company call the Flex-Wing.
This journal asked Ryan to outline the origin of the idea, and the
company replied, "I guess this Flex-Wing concept was originally
toyed with by Leonardo da Vinci—it seems he had a hand in every
revolutionary concept. There are also evidences that Otto Lilien-
thal had a hang glider concept which was close to the Flex-Wing
idea.
"However, the modern man credited with the wing is Francis
Rogallo. Now chief of a wind-tunnel branch of the National
Aeronautics and Space Administration, he has served NASA and
its predecessor NACA for 27 years, and 18 years ago began an
intensive study into what Ryan has since developed under the
registered name of Flex-Wing."
Ryan have used light-alloy structures and a variety of covering
materials. Ordinary rip-stock parachute nylon is common, or nylon
or Dacron covered with a plastic film to increase strength and reduce
porosity. These materials weigh from loz to 6oz per square yard,
and stand up excellently to repeated folding and general use. The
control mechanism shifts the position of the hung body relative to
the wing by reeling in and out the suspension lines on electro
mechanical winches.
The original free-flight, full-scale test vehicle was a manned
one. It was piloted by company chief engineering test pilot Lou
Everett, who found little difficulty in acquiring the special tech
niques needed to obtain the best results from such a concept.
Once Everett had shown that the Flex-Wing could be flown, he
undertook an intensive test programme for the US Army Trans
portation Research Command (TRECOM), at Brown Field, just
south of San Diego. The same craft was then shipped to the Nat
ional Aeronautics and Space Administration Langley Research
Center, in Virginia, where tests in Mr Rogallo's big open-jet tunnel
confirmed data obtained in free flight.
Ryan have thought of many Flex-Wing applications. Some
appear improbable, or at least not capable of immediate realization.
But during the past year a very encouraging number of these
potential applications have become the subject of US Government
contracts, including the following:—
1. Atmospheric recovery, following re-entry, of the NASA/Depart
ment of Defense Gemini two-man Earth orbiter (responsibility for this
part of the Gemini programme was not assigned to Ryan).
2. PDG (precision-drop glider) system for the US Army, using
Flex-Wings to support cargo containers released from transport aircraft
and remotely controlled to land on preselected spots.
3. ACD (air cargo delivery) system for the US Army, using Flex-
Wings to support gliders towed by helicopters.
4. Fleep (a corruption of "Flex-Wing" and "Jeep") for the US Army
TRECOM, using Flex-Wings to carry payloads in support of forward
troops.
5. Flex-Bee (a name stemming from the company's very successful
Firebee), for the US Marine Corps, using Flex-Wings to support an
unmanned reconnaissance package.
The last-named appears of doubtful value, since at first sight
A Ryan secretary provides scale to the diminutive Flex-Bee drone, an example of which is seen in flight on the right